Houston Astros catcher Max Stassi (12) before the start of the first inning of an MLB game at Minute Maid Park on Monday, Sept. 21, 2015. ( Karen Warren / Houston Chronicle ) Houston Astros catcher Max Stassi (12) before the start of the first inning of an MLB game at Minute Maid Park on Monday, Sept. 21, 2015. ( Karen Warren / Houston Chronicle ) Photo: Karen Warren, Staff Photo: Karen Warren, Staff Image 1 of / 9 Caption Close Astros activate Max Stassi from DL, option him to Class AAA 1 / 9 Back to Gallery

Max Stassi's rehab assignment is over. The Astros reinstated the 25-year-old catcher from the disabled list Sunday and optioned him to Class AAA Fresno, the affiliate he was already with as he worked his way back from March wrist surgery.

Stassi was expected to open the season as Jason Castro's primary backup before he underwent surgery during spring training to repair a fractured hamate bone in his left wrist. The Astros acquired journeyman Erik Kratz just before opening day to spell Castro, and he has just one hit - a bunt single - in 21 at-bats on the season.

Stassi likely will join the Astros soon, especially considering Castro is expected to go on the paternity list in the coming days. Stassi should benefit from more at-bats in Class AAA before a promotion. He has just two hits in 11 at-bats since joining the Grizzlies.

Castro has started 25 of the Astros' 32 games.